Direction Finding of rogue Wi-Fi access points using an off-the-shelf MIMO-OFDM receiver

Elimination of rogue Access Points (APs) is a challenging security goal of growing interest and practical importance. However, even when network administrators suspect that such devices are indeed present to attack their organization, physically locating their whereabout is an intricate task. In this work a method is suggested for implementing autonomous Direction Finding (DF), i.e., an apparatus for passively identifying the Angle-of-Arrival (AoA) of a received Wi-Fi signal, using a standard off-the-shelf Wi-Fi receiver. Modern wireless communication standards, such as Wi-Fi (e.g. IEEE 802.11n), are based on Orthogonal Frequency Division Multiplexing (OFDM) and Multiple-Input Multiple-Output (MIMO) technologies. The key contribution of the current work is an approach of employing the multiple receiving antennas jointly with OFDM Channel State Information (CSI) as the basis for implementing an interferometry DF tool. This approach is theoretically investigated via numeric analysis, and practically validated by a working prototype. The performance of the prototype was evaluated both in the laboratory, in a sterile environment, as well as in field trials. In realistic indoor setting the prototype was able to acquire the AoA with a median error of 8-15 degrees.